Arachidonic acid is known to be the biological precursor of several groups of biologically active endogenous metabolites. The first step in the metabolism of arachidonic acid is its release from membrane phospholipids, via the action of phospholipase A.sub.2. Arachidonic acid is then metabolized either by cyclooxygenase to produce prostaglandins including prostacyclin, and thromboxanes or by lipoxygenase to generate hydroperoxy fatty acids which may be further converted to the leukotrienes.
The leukotrienes are extremely potent substances which elicit a wide variety of biological effects, often in the nanomolar to picomolar concentration range. The peptidoleukotrienes (LTC.sub.4, LTD.sub.4, LTE.sub.4) are important bronchoconstrictors and vaso-constrictors, and also cause plasma extravasation by increasing capillary permeability. LTB.sub.4 is a potent chemotactic agent, enhancing the influx of leukocytes and inducing their subsequent degranulation at the site of inflammation. A pathophysiological role for leukotrienes has been implicated in a number of human disease states including asthma and related obstructive airway diseases, allergic rhinitis, rheumatoid arthritis and gout, psoriasis and atopic dermatitis, adult respiratory distress syndrome (ARDS), inflammatory bowel diseases (e.g. Crohn's disease), endotoxin shock, atherosclerosis and cardiovascular disorders (e.g. ischemia-induced myocardial injury) and glomerular nephritis. Any agent that inhibits the action of 5-lipoxygenase is expected to be of considerable therapeutic value for the treatment of acute and chronic inflammatory conditions.
For a review article on lipoxygenase inhibitors, see H. Masamune and L. S. Melvin, Sr.: Annual Reports in Medicinal Chemistry, 1989, 24, pp 71-80 (Academic). More recently, further examples of lipoxygenase inhibitors have been disclosed in WO 95/03309 and WO94/29299.